[10.04] Gravity Waves As A Probe Of Jupiter's Atmosphere

T. Bosak, A. P. Ingersoll (California Institute of Technology)

Vertically propagating waves carry indirect information
about the dynamic and static stability of Jupiter's deep
atmosphere. We are using mesoscale waves observed as linear
wave patterns in jovian clouds with wavelength clustered
around 300km (Flasar and Gierasch,
J.Atmos.Sci.,43,2683-2707,1986) as a probe of dynamical and
thermal conditions in the otherwise unobservable regions.
Time sequences of the Galileo images show that the waves
move relative to the background zonal flow.

Ingersoll and Koerner (Bull. Am. Astron. Soc., 21,943,1989)
suggested shear instability as the mechanism that selects
the preferred wavelength of the features. The deep vertical
shear layer extending from about 0.4 bars to about 5 bars
and static stability as measured by the Galileo probe
allowed us to test this hypothesis quantitatively. We are
numerically analyzing linear stability of gravity waves with
non-zero horizontal phase speeds in atmospheric conditions
constrained by the probe measurements.

We have found that, if the static stability in the shear
layer is very low (but positive), a strong and deep vertical
shear of the zonal wind as measured by the Galileo probe
(Atkinson, D.H., et al., JGR, 103, 22911-22928,1998) can
generate propagating gravity wave instabilities. Very small
values of static stability that support the development of
the instabilities are within the range of values measured by
the Galileo probe as interpreted by Seiff et al. (JGR, 103,
22857-22889,1998). The largest growth rates of the unstable
modes are of the order of hours, and their horizontal
wavelengths are 350±100 km. There is a good match between
the modeled and the observed wavelengths and timescale of
the waves.

The author(s) of this abstract have provided an email address
for comments about the abstract:
tbosak@gps.caltech.edu